Multicast and broadcast service in IEEE802.16j standard defines a relay method of multicast data in a system including relay stations arranged between a base station and wireless terminals. The base station receives multicast data via a wired network, and then wirelessly transmits the multicast data to the relay station controlled thereby. The base station and the relay stations work on the same frequency, and broadcasts the data to the wireless terminals thereof.
Wireless ad-hoc networks where data is wirelessly relayed for communications without wired line have been recently studied. FIG. 14 illustrates a wireless ad-hoc network in a related art. The network in FIG. 14 includes relay stations 101-103 and wireless terminals 111-114. Each of the relay stations 101-103 relays data transmitted by one of the wireless terminals 111-114 and then transmits the data to another of the wireless terminals 111-114. If the wireless terminal 114 transmits data to the wireless terminal 111, the relay stations 101 and 103 relay the data of the wireless terminal 114, and then wirelessly transmit the data to the wireless terminal 111. There are cases where the wireless terminals 111-114 themselves relay data.
If the IEEE802.16j standard (IEEE Std 802.16-2009) is applied to multicast communication in the wireless ad-hoc network, all the relay stations 101-103 can broadcast data to the wireless terminals 111-114 on the same frequency. For example, the relay station 101 may perform an operation corresponding to a base station complying with IEEE802.16j, thereby scheduling the multicast data. The wireless terminal 114 may serve as a terminal transmitting the multicast data.
Upon receiving the multicast data from the wireless terminal 114, the relay station 101 performs a scheduling operation such that the multicast data is broadcasted by the relay stations 101-103 on the same frequency. The relay station 101 transmits scheduling information and the data of the wireless terminal 114 to the other relay stations 102 and 103. The relay station 101 broadcasts the multicast data to the wireless terminals 113 and 114, controlled thereby, on the same frequency in accordance with the scheduling information generated by the relay station 101. The relay stations 102 and 103 broadcast the multicast data to the wireless terminals 111 and 112 respectively controlled thereby, on the same frequency in accordance with the scheduling information received from the relay station 101. In this way, the efficient use of wireless resources is improved, and reception quality of each of the wireless terminals 111-114 is thus improved.
Japanese Laid-open Patent Publication No. 2008-177969 describes an orthogonal frequency division multiple access (OFDMA) wireless system that autonomously performs interference free wireless relaying. Japanese Laid-open Patent Publication No. 2007-184935 describes an apparatus that relays transparently a signal in a multi-hop relay cellular network.